Reading Activity Week #5 (Due Monday)

Chapter V "The Perception of Color" was pretty interesting. The basic thing to know about color perception that humans see a narrow range of the electromagnetic spectrum between the wavelengths of about 400 and 700 nanometers. Most of the light that we see is reflected light.
Interesting was discussion if everyone see colors the same way? There are many answer for it and many explanations. YEs, we can see colors the same way and no because 8% of the male population is color blind and 0.5% of female. ALso, another possibility is answer "maybe"- because there might be some disagreement about marginal colors. Also, due to cultural relativism( the idea that basic perceptual experiences may be determinated in part by the cultural environment).
Another subject that I was interested in was color vision in animals. Color vision is accomplished in different ways in different species. We, humans are trichromats, with three different types of photo receptors. Dogs are dichromats with two different photoreceptors. Chickens- surprisingly are tetrachroamts (4).
The least interesting topics were the history of trichromatic theory and discussion about opponent processes ( LATERAL geniculate nucleus and color-opponent cell).
To better understanding the subject of color vision would be good to know the basic principles of color perception and also about rod photorepcetor who are responsible of color vision.
I would like to talk more about animals and their color vision as well as color blindness and the causation of it.

color blindness
trichromatic theory of vision
opponent processes
lateral geniculate nucleus
color-opponent cell
cultural relativism

The first thing that I found interesting in chapter five was also the topic about the basic principles of color perception. We learn early in the chapter that humans see a narrow range of the electromagnetic spectrum between the wavelengths of about 400 to 700 nm. Most of the light that we see is reflected light, meaning things around us that emit wavelengths reflect off of surfaces. The color of a surface depends on the mix of wavelengths that reach the eye from the surface. Different wavelengths of light give rise to different experiences of color. However, a single photoreceptor is completely ambiguous due to an infinite set of different wavelength-intensity combination's that elicit exactly the same responses. This cause problems for the photoreceptor and it cannot by itself adequately indicate either the wavelength or the intensity of a light. This is known as the problem of univariance (The fact that an infinite set of different wavelength-intensity combination's can elicit exactly the same response from a single type of photoreceptor. One photoreceptor type cannot make discrimination based on wavelength). Trichromacy (Trichromatic theory or color vision) is defined in the text as the theory that the color of any light is defined in our visual system by the relationships between a set of three numbers, the outputs of three receptor types now known to be the three cones. Trichromacy is based on the fact that humans see color by using a combination of three cone types. We have previously learned that there are two types of photoreceptors rods and cones. Rods are used primarily in low (scotopic) lighting while cones are used for bright lighting and color vision. The three different types of cones are short-wavelength cones (S-cones) which peak at about 440nm. Middle-wavelength cones (M-cones) peak at about 535nm and Long-wavelengths (L-cones) peak at about 565nm. S-cones are correlated with the color blue, M-cones with the color green, and L-cones with the color red. The advantage to having three cone types is that we can tell the difference between lights of different wavelengths. Some animals are dichromatic, meaning they only have two different types of cones, and other animals are tetrachromatic meaning they have four different types of cones.

The second topic that I found interesting in this chapter was the section that discusses if everyone sees color the same way. There are a few different answers for this question. One answer is that we all see color the same way, in the perspective that we all have the same performance on standard measures of color vision. Another answer is no. This is due to the fact that some of the population experiences color blindness. There are several variations to color blindness (also called color-anaomalous). Deuteranope is an individual who suffers from color blindness that is due to the absence of M-cones. Protanope is an individual who suffers from color blindness that is due to the absence of L-cones. Tritanope is an individual who suffers from color blindness that is due to the absence of S-cones. Cone Monochromats are individuals with only one cone type, they are truly color blind. Rod Monochromats are individuals with no cones of any type, they are truly color blind and are visually impaired in bright light. The third answer to this question is we might all see color the same. Meaning we all agree on the basics.

One of the things that I found the least interesting in this chapter was the topic of metamers. Metamers are defined in the text as different mixtures of wavelengths that look identical, more generally, any pair of stimuli that are perceived as identical in spite of physical differences. An example given by the textbook is that if the mixture of red plus green light produces the same cone output as the single wavelength of yellow light, then the mixture and the single wavelength must look identical. The single wavelength that produces equal M-cone and L-cone activity will look yellow, and the red and green lights will mix to produce yellow. There are two things to keep in mind about metamers. First, mixing wavelengths does not change the physical wavelengths. and for the mixture of a red light and a green light to look perfectly yellow, we would have to have just the right red and just the right green.

Other topics in this chapter that I did not find very interesting were the topics of color space, and the history of trichromatic theory. Color space is defined as the three-dimensional space, esstablished because color perception is based on the outputs of three cone types the describes the set of all colors. Three dimensions which are used to describe color perception are hue (the chromatic aspect of color), saturation (The chromatic strength of a hue. white has zero saturation, pink is more saturated, and red is fully saturated) and brightness (the distance from black to color space). I didn't find these topics very interesting and had a hard time understanding where they fit in when discussing the perception of color.

The topic that I think is the most important when it comes to understanding the visual system is the topic of Trichromacy. In class there are a few topics that I would like to discuss in greater detail. These are Opponent color theory (the theory that perception of color is based on the output of three mechanisms, each of them on an opponency between two colors: red-green, blue-yellow, and black-white), color-opponent cells (a neuron whose output is based on a difference between sets of cones), and afterimages (a visual image seen after the stimulus has been removed).

Terms: Problem of Univariance, Univariance, Trichromacy, scotopic, S-cones, M-cones, L-cones, dichromatic, tetrachromatic, Metamers, color space, hue, saturation, brightness, deuteranope, protanope, tritanope, color-anomalous, cone monochromat, rod monochromat, opponent color theory, color-opponent cells, and afterimages.

The first topic from Ch. 5 that I found interesting was the readings on the Problem of Univeriance. The Problem of Univeriance is the concept that an infinite set of different wavelength–intensity combinations can elicit exactly the same response from a single type of photoreceptor. As we know the human retina contains two kinds of photoreceptors: rods and cones. One photoreceptor type cannot make color discriminations based on wavelength. The problem of univariance is that we want to be able to perceive two aspects of light rays—wavelength and amplitude—corresponding to color and brightness. However, a single type of cone can only provide one piece of information—a neural firing rate. In other words, the firing rate of the receptor cell varies in only one dimension (it is “univariate”), but we need to code for two dimensions. This problem is so serious that if we had only one type of cone in our retinae, we would not have color vision. Most color vision deficits arise because the affected person is missing one type of cone. There are three different types of cones. You ask “why does this matter” because each cone contains a slightly different photopigment. There is an S-cone that is preferentially sensitive to short wavelengths; colloquially known as a “blue cone.” The M-cone that is preferentially sensitive to middle wavelengths; colloquially known as a “green cone.” And last but not least the L-cone that is preferentially sensitive to long wavelengths; colloquially known as a “red cone.” If you had no M-cones in your retinae the pattern of response rates across the remaining two cone types (S- and L-cones) would be identical lights. For people with normal color vision, these two lights are easily discriminable. But this doesn’t stop there. There is a lot more that ties into the whole she-bang. What does it take to bug a cone/ and or rod. Light intensities that are bright enough to stimulate the cone receptors and bright enough to “saturate” the rod receptors is called Photopic. The light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors are scotopic. Bottom line you just can’t talk about the problem of Univeriance with our mentioning the whole family.

P.S. sorry rods that you didn’t get much attention but you only make a small yet important contribution in fairly dim light. I guess Mother Teresa does say we can do no great things, only small things with great love.

The Second topic from Ch. 5 that I found interesting was the readings on additive color mixture and subtractive color mixture. Wicked!! The additive color mixture is a mixture of lights and subtractive color mixture is a mixture of pigments. When two lights or pigments come together they cause light to be added or subtracted. Just seeing the visuals in figure 5.8 gives me a whole new perspective on how I look at things, for example, in a theater. Imagine that we have two spotlights, each emitting bright white light and both aimed at the same point on a projection screen. We could then place one filter in front of each spotlight (as in textbook Figure 5.8). What we would see on the screen would be an additive color mixture: the light wavelengths that pass through the two filters would be added together as they reflect off the screen and into our retinae. In fact, this is exactly how many projection televisions work, with red, green, and blue filters placed in front of three bright lights that project onto a screen. Alternatively, an RGB computer monitor is so named because it has three types of colored pixels: red, green, and blue. Any color that the computer displays is created by illuminating combinations of these three colored pixels at different intensities. Now if we back it up to figure 5.7 we can experience subtractive color mixture. Imagine that we take a single spotlight and aim it at a projection screen. We then place one filter so it blocks some of the light from the spotlight. Finally, we place another filter in front of the first filter. Now, only wavelengths that can pass through both filters will bounce off the screen and onto our retinae (as depicted in textbook Figure 5.7). This is one form of subtractive color mixing: the wavelengths blocked by the second filter are “subtracted” from the wavelengths that made it through the first filter. Paint mixing is a more familiar form of subtractive color. Here, each of the paints in the mixture subtracts out the light wavelengths that are absorbed by the paint; only wavelengths that are reflected by all of the paints arrive at your retinae. All I can think of is Willy Wonka’s Wonkavision. Just in case you want to see it… http://www.youtube.com/watch?v=GDLkXKQ1Ydo&feature=related it may not even go with the whole concept I just thought it was cool and my opinion. What do you think?

One topic I found the least attractive but it was still interesting was the information on the opponent cells in the lateral geniculate nucleus. The lateral geniculate nucleus (LGN) is a structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex. I actually was disappointed, they mentioned that earlier work on the combination of cone signals was done with fish but they gave the job to the monkeys, go figure. So I researched some information on these fishes so they can have their five minutes of fame. The experiments that brought Hering's opponent color theory to the forefront were done in fish retina by another Swede, Gunter Svaetichin (1956) using glass instead of metal electrodes, enabling him to record intra-cellularly from horizontal cells. This allowed him to see both depolarizing and hyperpolarizing responses, the latter not obvious with extra-cellular recordings, where one sees only a silence or perhaps an off response from inhibition (hyperpolarizing) which could easily be overlooked. Svaetichin's results gave rise to resurgence in Hering's opponent color theory this quickly led to the idea that there were three retinal channels representing Hering's color opponent channels, red opposing green, yellow opposing blue and white opposing black. This idea, however, was short lived. First of all it became apparent that the red/green opponent cells had concentrically organized receptive fields with the color opponent inputs coming from adjacent retinal regions. One would expect the color opponent signal should involve the same area of visual space and not neighboring areas. In addition the red-green opponent ganglion cells seemed to be the midget cell system which was the logical mediator of high spatial resolution. This created a dilemma in having red/green color opponent channel carrying achromatic information for high spatial resolution. In addition the S cone channel was opposed by yellow light but not strongly enough to stop responses to white. The S cone on ganglion cells appeared to be transmitting a signal that said that the S cones were absorbing light but not that this light was "blue"; it could be white, grey as well. The so called white/black channel was receiving no input from S cones which is not what is expected for a channel signaling white. The contribution of activation of the S cone retinal ganglion cells is illustrated by the after images produced.

My other not so attractive topic is the section on; does everyone see colors the same way? It is a really good question but if you really think about it without reading you would think well of course not we are all diverse. If you think yes then you are right! You may all look at green and say green but the nm will vary be between people. If you think no you are also right! There is this thing called color blindness, it is a form of color vision deficiency. Color blindness is typically caused by the congenital absence or abnormality of one cone type—usually the L- or M-cone, usually in males. Most color-blind individuals are not blind to differences in wavelength. Rather, their color perception is based on the outputs of two cone types instead of the normal three. There are a number of different types of color blindness. A deuteranope is an individual who suffers from color blindness that is due to the absence of M-cones. A protamine is someone who suffers from color blindness that is due to the absence of L-cones. A tritanope is someone with no S-cones. People genetically inherit three cone photopigments which is called color-anomalous, but two of them are so similar that these individuals experience the world in much the same was as individuals with only two come types. And last but not least of the different types of color blindness. A cone monochromat is an individual with only one cone type. Cone monochromats are truly color-blind. An individual with rod monochromat has no cones of any type. In addition to being truly color-blind, rod monochromats are badly visually impaired in bright light. Just to add in a little more info on the eye-ball; Agnosia is the failure to recognize objects in spite of the ability to see them. Agnosia is typically due to brain damage. Finally, anomia is the inability to name objects in spite of the ability to see and recognize them it is also typically due to brain damage.

What did I read in this chapter that I think will be most useful in understanding the history of psychology? Well maybe some insight on how to condition or trick my eyes in seeing differently. I could do some classical conditioning. Ivan Pavlov developed the procedures associated with classical conditioning. Ivan is part of the history of psychology.

dun dun du dunnn, the end is in sight!

Finally the two topics or concepts that I would like you to cover more in-depth in class. First the spectral reflectance function which is the function relating the wavelength of light to the percentage of that wavelength that is reflected from a surface. Last I would like to hear more about the concept of reflectance which is the percentage of light hitting a surface that is reflected and not absorbed into the surface. Typically reflectance is given as a function of wavelength.

Terms: Problem of Univeriance, photoreceptor, rods, cones, color discriminations, S-cone, M-cone, L-cone Photopic, scotopic, additive color mixture, subtractive color mixture, opponent cells, lateral geniculate nucleus, Hering's opponent color theory, color blindness, deuteranope, protamine, tritanope cone monochromat, Agnosia, anomia, history of psychology, spectral reflectance function

One topic that I found interesting was the idea of univariance. This is the idea that infinite set of different wavelength-intensity combinations can cause the exactly same response, so a single photoreceptor can not tell us anything about the wavelengths stimulating it. The problem is that 450nm of light will produce the same effect in the photoreceptor as 625nm of light does. The photoreceptor has no way of distinguishing them, but one is orange and is violet. The problem is even worse because we could take any mix of wavelengths and by adjusting the intensity get the exact same response out of the photoreceptor. Another topic that I found interesting was the topic on Trichromacy. In this section it talks about how our rods are sensitive to low light levels, which we already know, but they have only one type of photopigment which is called rhodospin. This means that they all have the same sensitivity to wavelength, which makes it impossible for rods to discriminate colors. This is why it is hard to see colors at night. Cones are the receptors that are sensitive to higher light levels; cones come with three different photopigments. The first one is S-cone, which is sensitive to short wavelengths and is sometimes known as the blue cone. Another is M-cone, which is sensitive to middle wavelengths and sometimes know as the green cone. Finally there is the L-cone which is sensitive to long wavelengths and is sometimes know as the red cone. These different types of cones help us overcome the univariance problem, by taking the input from the three different cones to differentiate wavelengths. One topic that I did not find very interesting was the problem with the illuminant. I found this topic fairly difficult to understand and not very interesting. Another topic that I did not find very interesting was the topic of physical constraints make constancy possible. Also with this topic I found it fairly difficult to understand the information presented. The topics that I think will be most helpful are the topics of Trichromacy and opponent processes. I would like to go over opponent processes and after images in class.

Terms
Problem of Univariance
S-Cone
M-cone
L-Cone

I find the idea that colors are just a result of the way we see and objects themselves do not have color to be incredible. As the author explains, color is psychophysical and not physical as evident by the way we see (or don’t see) color during the dark. As we know rods are photoreceptors that are sensitive to scotopic (low) light. This is because they contain the photopigment molecule rhodopsin. This problem of univariance(output of photoreceptor doesn’t tell us anything about wavelengths) ( due to rhodopsin ) makes seeing color at night difficult.
It is interesting how the author contrast this with the way that we see during the day. The photoreceptor cones are for seeing during photopic light ( daylight) and there are three kinds: S-cones (short wavelength/~blue), m-cones (middlewavelenths/~green), and L- cones (long wavelengths/~red). The variety of types of cones with different photopigments allow us differentiate between different wavelengths of light.
I also found the evolution of animal color vision to be interesting. I had no idea there was that much evolutionary convergence with color vision. The authors say that color vision can prove useful in eating and sex. They go on to explain that it would prove helpful in selecting ripe fruit for example, as well as the sexual selection process. I would like to talk more about the development of color vision as well as color blindness because they are interesting to me. I liked the discussion of Anomia least it is a strange disorder that I don’t quite understand. From what I got is they can see the colors but can’t name them, how is this visual problem? I also did not enjoy cultural relativism as much because it seemed a bit obvious which made it less interesting.
Terms: scotopic, rod, rhodopsin, problem of univariance, photopic light, s-cones, m-cones, l-cones

I thought the topic of Trichromacy was interesting. As the book states, we learned about color in chapter to. Color has been one of my favorite topics so far. The retina has two types of photorecptors which as we know are rods and cones. Rods are sensitive to low (scotopic) light and contain one type of photopigment molecule called rhodopsin. We don't see as much color in the dim light because this dim light stimulates only the rods which can only have sensitivity to one wavelength. Therefore, it cannot detect color. Cones, however, come in three different types with different photopigments and wavelengths. They can see the daylight levels (photopic).These cones are called S-cones (short wavelength, 440 nm), M-cones (medium wavelength, 535 nm), and L-Cones (long wavelength, 565 nm). We perceive the long to be red, medium to be green, and short to be blue. However, if we had only L cones, we would not see red because of the problem of univarience, which is the fact that one photorecptor alone cannot create color.We can make any wavelength look like another by adjusting the intensity of light. A specific light produces a set of responses from the human cone types, however. The relationships between the cones are what defines the color. This is what trichromacy is.
Another topic I found interesting was whether everyone sees colors the same way. This stated that there will be some variation, but for the most part it will be the same. Many males have a form of color vision deficiency known as color blindness. This is when there is a malfunction in one or more of the genes that code the photopigments of the three cones. This gene is on the X chromosome, and since males only have one copy of the X chromosome if one is defective then they will have an issue. These are the M and L cones that are on the X chromosome. There are also different types of color blindness. Some factors include the type of cone affected, the type of defect (photopigment is anomalous, or different from the norm), or the cone type is missing altogether. This doesn't mean they cannot see all colors. They may see a few colors a little differently with color blindness. They have trouble seeing color in the middle to long wavelength. Having no M-cones is called deuteranope. Protanope is soneone who has no L-cones. Tritanope has no S-cones. Color anomalous is just a term for color-blind as well. True color blindness, which I thought was intersting, is called cone monochromat, and this is when they only have one type of cone in the retina. The rod monochromat is when a person is missing all cones, and these people have a very hard time seeing detail during the day at all.
I thought the topic of three numbers, many colors, was a little more unintersting to me. With our three little types of cones we can gather about 10 million different colors, which is amazing.With the three numbers of each cone type, we can define three dimensions of a color space. We use terms such as hue, saturation, and brightness to define color. Hue is the colorful, or chromatic, aspect of color. Saturation is the chromatic strength of a hue. (White has 0 saturation, pink is a little more saturated, and red is fully saturated). Brightness is the distance from black (zero brightness) in color space.
A second not-so-interesting topic was color constancy. Above was stated that unrelated color is a color that can be experienced in isolation. This did not include brown or gray, which is called a related color. These are seen only in relation to other colors. With color constancy, the illuminant is the light that lights up a surface, while the spectral reflectance function is the percent of the wavelength that's reflected from the surface. The spectral power distribution, however, is the amount of light at different visible wavelengths.
I'd like to cover the topic of color vision in animals and trichromacy a little more because I thought those topics were very interesting. I just find the color topic so interesting!

The first thing I found interesting was that of color perception. Most of the light that we see if reflected light. Some wavelengths are absorbed by the surfaces they hit. The more light that is absorbed; the darker the surface will appear. Other wavelengths are reflected and some of that reflected light reaches the eyes. The color of a surface depends on the mix of wavelengths that reach the eye from the surface. In addition, one kind of human photoreceptor responds to light of a specific wavelength while the intensity of the light is held constant. 400nm light produces only a small response in each cell, 500nm light produces a greater response and 550nm light even more. However, 600nm light produces less than the maximal responses and 650nm light produces a minimal response. Light of 625nm produces a response of moderate strength. When it comes to seeing color, the output of a single photoreceptor is completely ambiguous. As infinite set of different wavelength intensity combination can elicit exactly the same response, so the output of a single photoreceptor cannot by itself tell us anything about the wavelengths stimulating it, which is know as the problem of univariance, which univariance explains the lack of color in dimly lit scenes. Moreover when it comes to lights, filters and finger paints there are two types of mixture. First is considered the additive color mixture where you take one wavelength or set of wavelengths and add it to another. A mixture of lights, if light A and light B are both reflected from a surface to the eye, in the perception of color the effects of those two lights add together. Whereas, subtractive color mixture, a mixture of pigments. If pigments A and B mix, some of the light shining on the surface will be subtracted by A and some by B. only the remainder contributes to the perception of color. There is color space, which is 3D space, established because color perception is based on the outputs of three cone types that describe the set of all color. This consists of hue, the chromatic (colorful) aspect of color, saturation, the chromatic strength of a hue. White has zero saturation, pink is more saturated and red if fully saturated, and brightness, the distance from black (zero brightness) in color space.

The second concept I found intriguing is opponent processes. Lateral geniculate nucleus is a structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connection to the visual cortex. Ganglion cells in the retina and the LGN of the thalamus are maximally stimulated by spots of light. These cells have receptive fields with a characteristic center surround organization. Fro example, some cells are excited when a light turns on in the central part of their receptive fields and inhibited when a light turns on in the surround. L and M cells seem to work similar together in their sensitivities. L-M cells are one type of color opponent cell, meaning chromatic information is pitted against the other one. The cells that were excited by light onset could be thought at L+M cells. Another way to see opponent colors in action is to look at negative afterimages, which are a visual image seen after the stimulus has been removed. The first colored stimulus is called the adapting stimulus which removal produces a change in visual perception or sensitivity. The illusory color that is seen afterward is the negative afterimage which states that an afterimage whose polarity is the opposite of the original stimulus. Light stimuli produce dark negative afterimages. Colors are complementary; for example, red produces green and yellow produces blue. There is also a neutral point at which an opponent color mechanism is generation no signal.

One thing I found least interesting was how individuals see color the same way or not. When it comes to (yes) everyone sees colors the same way it depends on individuals such as their age being a factor because their unique green will turn the lens of the eye yellow with age. However, ones performance on standard measure of color vision will be the same as others’. When it comes to the (No) part color blindness could be the problem which happens more often in males since they have only one X chromosome and if their other chromosome is impaired then this might result. Females have two copies and can have normal color vision even if one copy is abnormal. There are a number of different types of color blindness. One determining factor is the type of cone affected, a second factor is the type of defect; either the photopigment for the cone type is “anomalous” that is, different from the norm, or the cone type is missing altogether. If you have two cone types rather than three, the normally 3D color space becomes a 2D space. If you have all three cones, you need three primary colors to make a metameric match with an arbitrary patch of color. Most color blind individual have difficulty discriminating lights in the middle to long range wavelengths. Someone who has no M cones is considered deuteranope. Their photoreceptor output to two lights will be identical. Someone who have no L cones will have a different set of color matches based on the outputs of his two con types S and M cones, known at protanope. Tritanope is where someone is with no S cones. Genetic factors can also make people color anomalous. Color anomalous people typically have three cone photopigments, but two of them are so similar that these individuals experience the world in much the same way as people with only two cone types. True color blindness comes in a few rare forms. Its possible to be a cone monochromat, with only one type of cone in the retina. Cone monochromats live in a 1D color space, seeing the world only in shades of gray. Even more visually cripples is the rod monochromat, who are missing cones altogether. Two other things that come about are agnosia, where the patient can see something but fails to know what it is and anomia which is the inability to see colors. Moreover, when it comes to people maybe seeing the same colors, there a thing called cultural relativism meaning that each group is free to create is own linguistic map of color space. In other cultures they have different numbers of basic color terms in different languages meant that color categorization was arbitrary.

The second least intriguing concept was that of color of lights to the world of color. A color that can be experienced in isolation is an unrelated color. For example, nothing will explain brown or gray because there is no such thing as an unrelated light that appears brown or gray. Brown, gray and a host of other colors exist only as related colors, colors that can be seen only in the context of other colors. The color we see on one object depends in complex ways on the colors of other objects vicinity. When it comes to luminance change without hue change looks like a shadow, whereas luminance change with hue change looks less like a shadow. Moreover, real surfaces tend to be broadband in their reflectances which is the percentage of light hitting a surface that is reflected and not absorbed into the surface. Typically reflectance is given as a function of wavelength. Even surfaces that are nearly metameric with single wavelenths of light are actually reflecting a wide range of wavelengths.

What I think would be most useful in understanding the visual system is color in the visual cortex and trichromacy. Trichromacy by definition is the theory that the color of any light is defined in our visual system by the relationships of three numbers, the outputs of three receptor types now know to be the three cones. The three cones go by sensitivity to wavelength. Short-wavelength cones (s-cones) are sensitive to short wavelengths, whereas M cones are sensitive to medium wavelengths and L cones are sensitive to long wavelengths. Moreover, when it comes to rods and cones, rods are sensitive to low (scotopic) light levels. All rods contain the same type of photopigment molecule: rhodopsin. Thus, they all have the same sensitivity wavelengths. Scotopic is light intensities that are bright enough to simulate the rod receptors but too dim to stimulate the cone receptors. On the other hand, cone photoreceptors are sensitive to higher, daylight light levels (photopic). Cones come in three varieties, each containing a slightly different photopigment. These different pigments give each type of cone distinctive wavelength sensitivity which I discussed above. Photopic is light intensities that are bright enough to stimulate the cone receptors and bright enough to saturate the rod receptors. Cones sensitive to long wavelengths are pitted against medium wavelength cones to create an L-M process that is roughly sensitive to the redness or greenness of a region. L+M cones are pitted against short wavelength cones to create a process roughly sensitive to the blueness or yellowness of a region.

The two topics I would like discussed more in depth are achromatospsia and color constancy. Mechanisms of color constancy use implicit knowledge about the world to correct for the influence of different illuminants and to keep the strawberry looking red under a wide range of conditions. Color constancy is the tendency of a surface to appear the same color under a fairly wide range of illuminants Illuminant is the light that illuminated a surface. Spectral reflectance function related to the wavelength of light to the percentage of that wavelength that is reflected from a surface. Spectral power distribution is the physical energy in a light as a function of wavelength. There are two different type of daylight: sunlight and skylight. Sunlight is a yellowish light, richer in middle and long wavelengths; skylight is more bluish.. Achromatopsia is the inability to perceive colors that are caused by damage to the central nervous system.

Key Terms: achromatopsia, trichromacy, problem of univariance, S cones, M cones, L cones, scoptic, photopic, cones, rods, color space, hue, saturation, brightness, subtractive color mixture, additive color mixture, ganglion cells, lateral geniculate nucleus, color opponent cell, neutral point, negative afterimage, afterimage, adapting stimulus, agnosia, anomia, rod monochromat, cone monochromat, protanope, tritanope, color anomalous, deuteranope, cultural relativism, unrelated colors, related colors, reflectances, color constancy.

Two things I found interesting from chapter 5 was the concept of S, M, and L cones. These stand for short, medium and long, respectively. I find these interesting because each cone is activated only when a certain length of a wavelength are perceived. Each cone has peak sensitivity. The wavelengths 450 nm to 625 nm are the M-cone but they produce different outputs in the L and S-cones. I find this interesting because even though our visual system is complicated, this aspect is broken down to just small, medium, and long cones.

Another thing I found interesting is cone monochromat. If you are a cone monochromat, you are completely color-blind. This occurs because they only have one type of cone. With only one type of cone, they can only see the world in shades of grey. I think this is interesting because I couldn’t imagine living in a world without color. It reminds me of the book “The Giver”, a story about a different type of world in which color has been taken. It also makes me think about animals that are color-blind which must mean that animals, like dogs, only have one type of cone.

One thing I found least interesting is the history of how certain theories came about, like the trichromacy and opponent color theory only because I don’t think history is boring and although it gives information as to how the theory came about, it’s not as useful to understand the concepts. Another thing I found uninteresting is metamers because I don’t think it makes sense and I don’t think the concept adds to my understanding of the perception of color.

Some information in this chapter that’s useful to understanding the history of psychology is the thrichromatic theory of color vision, also known as the Young-Helmholtz theory. Thomas young and Hermann von Helmholtz figured out that light is defined by the outputs of three receptor types, called the cones. This happened in the 1800s. Another theory called the opponent color theory was created by Ewald Hering that stated there were four basic colors in two opponent pairs: red-green and blue-yellow. Knowing these theories helps understand the history of psychology because it shows that physics is an important part in the development of our modern psychology.

Terms: thrichromatic theory of color vision, cones, opponent color theory, metamers, cone monochromat, S, M, L-cones, wavelengths

The trichromatic theory of color vision explains that our ability to perceive color is due to the fact that we have cone receptors specifically tuned to a particular light frequency. Rods acts as sort of light detectors. Light stimulates them and they fire, sending a simple "yes light is present" to the next cell. Cones are different because they are sensitive to frequency. When light strikes a cone it only sends a message on further down the system if it is tuned to respond to that frequency of light. Each of the three types of cones are sensitive to a range of frequencies. Graphs representing the distributions of frequency sensitivity show that each type, when graphed, resembles a normal curve almost. That means there is an ascent, a peak, and a descent in firing rate as you increase or decrease frequency. Cones are either classified as S-cones, M-cones, or L-cones. These stand for short wavelength, medium wavelength and long wavelength, respectively. Short wavelength means a higher frequency, and higher energy. Blue light is often associated with short wavelength. Medium wavelengths are greens and greenish yellows and long wavelengths correspond to red light. The trichromatic theory holds that differing response rates in our collection of cones is what allows us to perceive color. If we are stimulated by a light each cone responds at a rate that is dependent on what frequency that cone is tuned to and what frequency the light entering the eye has. If the light is red the L cones will respond at a very high rate, and the M cones will respond but at much lower rate. S cones may or may not even respond but their rate would be very low. Because we have these three sort of "color meters" our brains are able to organize the information received by the cones. Cones, just like all receptors, operate in such a way that the message sent on to the next cell is not "I see red light" but it is "I am being very much stimulated." So in the case of the red light L cones are going wild and our brain senses that their must be a light source. Without the other two types of cones this is probably the only information the brain would really be ale to perceive. When the brain sees that the rate of response from all the M cones is less than that of L cones, (and s cones are much less) by process of elimination it assumes that the light stimulating the eye must be low wavelength. Intensity of light greatly affects cone response rates. That is why we have poor color vision at night. But light intensity does not alter the ratio of response rates by the three sensitivity distributions. Just like we have been discussing all semester the visual system is built to operate on contrast. It measures the difference in response rates between the 3 types of frequency sensitivities. So what happens when the three measurement devices get the same reading. A metamer is a mixture of multiple wavelengths of light that stimulate the cones in such a way that they respond in the exact same way as they would being stimulated by another wavelength. As i said before the visual system is concerned with the difference between the systems. So if the systems are stimulated in the same way, no matter if it is one yellow light or a red light and a green light mixture, we will perceive the same color. 10-5-1=4, and 10-2-4=4. This is how our brain may view cone response. It sees three readings of a light source and can only tell you the difference.

Chapter 5 is about the perception of color and color vision. First, most of the light we see is reflected light. Color is a creation of the mind, it is not a physical property. This chapter talked a lot about the problem of univariance. Univariance explains the lack of color in dimly lit situations. The problem of univarance makes it impossible to tell colors in dimly lit situations. This problem proves that color is not a physical property. The reason for the problem is because in dim light situations we are basically only seeing with our rods and not our cones. Moreover, different wavelengths of light give rise to different experiences of color. The problem of univariance also has to do with the thichromacy. The Trichromacy has to do with rods and cones. Rods deal with scoptic light. Scoptic light is light that is dim. Cones come in three forms. This is where things really get interesting. The three forms are shot-wavelength cones (s-cones), middle wavelength cones (m-cones), and long-wavelength cones (l-cones). Having three types of cones allows us to tell the difference between lights of different wavelengths. The combination of all three cone types is where color vision begins. The trichromatic theory of color vision, also known as the Young-Helmholtz theory states that color of light is defined in our visual system by the relationships among three numbers. Metamers have something to do with the perception of color. Moreover, the chapter goes on to talk about additive color mixture and subtractive color mixture. First, additive color mixture is a mixture of lights. Next, subtractive color mixture is a mixture of pigments.
As stated earlier, color vision is based on the out of the three types of cone photoreceptors. One thing that really blew my mind was that our visual system can make about 10 million colors from these three types of cones!! Hue, saturation, and brightness are all terms that I have heard before but never really knew what they meant. Hue is the colorful aspect of color. Saturation is the strength of hue. And Brightness is the distance from black in color space. One example of hue, saturation, and color is the box on our computer that we can adjust all three things.
There are also some opponent processes. Some opponent processes are beyond trichromacy, Beyond Trichromacyopponent cells in the lateral geniculate nucleolus, psychophysical roots of color theory, and color in the visual cortex. First, Opponent cells in the lateral geniculate nucleus (LGN). LGN is in the thalamus and it receives input from the retinal ganglion cells and has input and output connections to the visual cortex. In the LGN are color-opponent cells. These are neurons whose outputs are based on differences between sets of cones. Moreover, there is also an opponent color theory. This theory basically states that each of the colors are opponents to each other. Within the psychophysical roots of opponent color theory are unique blue and unique hue. Unique blue is a blue that has no tint of red or green. Unique hue on the other hand is a color that can be described with a single term. Examples are red, blue, green, and yellow. After images are also talked about while talking about opponent colors. Afterimages are a visual image seen after the stimulus has been removed. Negative after images also play a role. Negative afterimages have the opposite of the original stimulus. Ex. light produce dark negative after images.
Color blindness was a section in this chapter that is very interesting to me. It opened my eyes to a lot of truth about color blindness. Color blindness is more likely to affect men than women.8% of the male population are color blind, while only .5% are color blind. Color blindness is a malfunction in one or more of the genes coding the three cone photopigments. The reason it is more common in guys is because we only have one X chromosome. There are different types of colorblindness. Sometime we think that people who are missing one cone type are colorblind. But this is not necessarily true, because they can still see some color. If we have two cones and not three, the colorspace that is usually three dimensional becomes two dimensional. The first type of colorblindness is deuteranope. This is a person who has no M-cones. The second type of colorblindness is protanope. This is a person who has no L-cones. The third type of colorblindness is tritanope. This is a person with no S-cones. Color-anamalous can be caused by genetic factors. Color-anomalous is simply a better term for color-blindess. Next, cone monochromat is a person with only one cone type in the retina. These are people who see the world in shades of grey. Even worse, rod monochromat are people who are missing cones all together.Finally, Aschromatopsia is a loss of color vision after brain damage. Some pieces in our cortex are vital for the way we perceive color.
Next, I will talk about from the color of lights to a world of color. First, unrelated colors are colored lights in isolation. Second, related colors are colors that can be seen in context with other colors. Ex. brown. Illuminant is something that we cannot ignore when talking about colors. This is the amount of light that illuminates a surface. I found color consistency to be pretty interesting. Color consistency is the tendency of a surface to stay fairly consistent under a large range of illuminants. I also found reflectance to be fairly interesting. This is the amount of light that hits then surface and then is reflected off. This is a problem with the illuminant.